Grip heaters are employed to heat the hand grips of motorcycles, snowmobiles, and similar equipment which are operated in cold weather but which require sufficient dexterity on the part of the user to make the wearing of bulky mittens or gloves impractical. Such grip heaters are particularly beneficial in alleviating the effect of wind chill, especially when used on vehicle handgrips. These grip heaters have an electrical heating element which is embedded in the handgrip and is powered by a voltage supply of the equipment, such as a battery or a magneto. Examples of such grip heaters are taught in U.S. Pat. Nos. 4,471,209; 4,937,429; and 4,990,753 of the present inventor. These grip heaters have a single heating element of resistive wire wrapped over a tubular insulator having a pair of helical recesses in which the heating element resides. This structure is subsequently covered with a soft grippable material such as rubber to form a composite grip; the helical recesses serve to maintain the heating element in place as the soft grippable material is molded onto the wire-wound insulator. When an electrical current is passed through the wire of the composite grip, the grip is heated.
Since equipment with grip heaters are typically operated under a wide range of temperature and operating conditions, there is frequently a desire to adjust the amount of heat provided, such as providing both a low heat setting and a high heat setting. One approach to providing different degrees of heating is to provide two different heating elements in the handgrip, each element generating a different amount of heat when powered by the equipment battery. This has been achieved through the use of heating elements fabricated with printed circuits, where a pattern of conductors can be printed so as to form two interleaved but electrically isolated circuits on a substrate, which is then formed into a tube and incorporated into a grip. The printed circuits maintain reasonable grip thickness since the conductors are thin and flat; however, these conductors tend to break down at one or more locations along the conduction during use. These breakdowns may result from damage to the printed circuits due, in part, to mechanical straining of the circuit by the user applying force or torque to the grip to maneuver the device to which it is attached. The mechanical strains introduce irregularities which in turn causes the temperature to spike, causing local deterioration of the circuit and ultimately failure; this limits the useful life of such devices. Two additional problems that have been found in printed circuit grip heaters are delamination and heat loss. Over time, the circuit substrate delaminates from the underlying structure, apparently due to thermal degradation of the laminating adhesive, again reducing the life of the grip. The printed circuit also results in excessive heat loss since it resides in close proximity to a metal handlebar and employs flat conductors wrapped around the handlebar, which will increase heat radiation toward the handlebar.
U.S. Pat. No. 6,686,572 teaches a grip heater having two heat levels which does not require the use of printed circuits. The '572 patent teaches a heated handle having a tubular insulator with two interposed helical coils wound thereon, the coils having different heating efficiencies. The coils reside in a pair of parallel helical recesses in the tubular insulator and are subsequently covered with a rubber jacket to form the handle. The '572 patent does not disclose how the individual heating coils are connected to form a circuit, thus raising the issue of whether the '572 patent provides an enabling disclosure. However, while not taught in the '572 patent, it appears that a circuit could be formed if each of the coils is connected to a metal handlebar which in turn is connected to the ground terminal of the battery. In fact, this approach has been commercially used in dual-coil heated handgrips offered by Polly Heaters, Inc. of Franklin Park, Ill., at least as early as 1998. The Polly Heaters handgrips employ two heating elements that are connected to a switch for power from the equipment battery at one end of the handgrip and connected to a central metal sleeve at the other end, which provides a ground through the metal handlebar of the equipment. The switch allows either of the heating elements to be energized, to provide either a low or high heat output. A limitation of such grip heaters is that they depend on the central metal sleeve and metal handlebar to complete the electrical circuit, and thus cannot be used on equipment which has handlebars that are electrically insulated from the battery. Additionally, the metal sleeve tends to act as a heat sink, drawing heat towards the metal handlebars.
An alternative approach to provide a grip with a variable heat output is to control the amount of heat generated by a single heating element. This has been achieved either by limiting the electrical voltage available to the heating element or by varying the amount of time that the heating element receives power. Limiting the voltage available to the heating element, so as to provide a low heat setting, is accomplished by a resistor and a switch. When the switch is in its low heat position, the resistor is in series with the heating element, and when the switch is in the high heat position, it bypasses the resistor. The inclusion of a resistor complicates the wiring and results in wasted electrical power output. Furthermore, the resistor must be fairly large to dissipate a large amount of energy and must be mounted in an exposed location to allow the heat to be dissipated, complicating installation of the grip heater. Controlling the amount of time that the heating element is energized is typically achieved by use of a Pulse Width Modulator, where the electrical current is rapidly pulsed on and off, with the proportion of time on determining how much heat is provided. This approach requires complicated circuitry to switch the current on and off.
Thus, there is a need for a grip heater that allows selecting between high and low heat output while avoiding the disadvantages of the prior art.